This project is directed toward furthering the understanding of the basic scattering mechanisms of ultrasound in biological tissues including blood and genesis of textural patterns of tissues in B-mode ultrasonograms. This information is crucial to the better interpretation of ultrasonic images obtained by commercial scanners and to the realization of quantitative characterization of the state of the tissues by ultrasound. More data will be needed to validate our hypothesis that ultrasonic backscatter or echogenicity of a tissue is related not only to its biological composition but also to the sizes of structural components in that tissue or to the size of the most dominant structure in that tissue as a first approximation. The results obtained from blood scattering measurements indicating that ultrasonic backscatter from blood is affected by the shear rate, hematocrit, flow disturbance, and a plasma protein, fibrinogen will be validated by Doppler measurements. If these data are demonstrated to be true with Doppler methods, then generally accepted assumption in analyzing Doppler data that Doppler signal level at a frequency is proportional to the number of red cells moving at that velocity will have to be modified. This may have a profound impact on the interpretation of results obtained by Doppler devices and may shed some light as to the future applications of Doppler ultrasound. Our initial results on blood scattering also show that ultrasound may be a promising new approach for performing a number of hematological tests such as red cell and platelet aggregometry and coagulation time measurements. In the next grant period, this effort will be continued. Ultrasonic backscatter measurements will be made using both the narrowband and the wideband substitution approaches. backscatter results will be correlated to histological analysis. Tissue structural size analysis will be performed with a computerized microscopic image processing system.